I need to vent: expansion tank split

[dykaar]

As part of a preventative maintenance effort, I replaced the coolant expansion tank. I had already replaced the rad after finding a pinhole leak in the upper hose coupling elbow. Guess I'll put the old tank back in.

I had a split in the 22 year old expansion tank on my e28 535 tank and I just patched with silicone seal. This one split at what looks like the mold joint. I'll post a pic when its out.

Yes I know this is the Achilles heel of e39s, but the original went 9 years without failing and the replacement lasted less than 2. Feh.

[chiefwej]

One suggestion.....Evans NPG+ (http://forums.bimmerforums.com/forum/showthread.php?t=1466277&highlight=zero).

[dykaar]

OK, so tell me what is it that regulates the pressure in the e39 cooling system?

[Schitzo]

OK, so tell me what is it that regulates the pressure in the e39 cooling system?

the cap on the reservior, rated at 2 bar.

[dykaar]

OK, I googled, but thanks. So with no traces of coolant around the cap, either I'm below 2 bar and the expansion tank split anyway, or the cap is failed closed. I didn't replace it when I replaced the tank. Do the caps fail closed?

I had a fuel pressure regulator fail closed on e28 535 and the mechanic said the pressure reading was off scale...

[AnotherGeezer]

I had a new/replacement Behr tank leak on me. My mechanic said it was common to get a dud from time to time.

[dykaar]

"dud" means "infant mortality". In other words the part fails immediately because the inspections/testing done at the factory were insufficient (or worse, non existent or ignored). Or the part failed because the design spec was insufficient, e.g. the spec was for one bar and the implementation was two bar. Even so, a burst pressure that is so close to the operating pressure, AND isn't tested seems crazy.

We all know the cooling system is a weak link, its just annoying to discover how weak. I may try fixing the old tank if I get mad enough.

[AnotherGeezer]

I didn't take the the defective part personally.

Stuff happens, especially when it's made of plastic.

[dykaar]

That's not very comforting when the plastic content of cars is increasing with each generation. You'd think that the design would take into account the change of materials, and that the engineers would get up to speed on the materials properties. Sheesh. I do take it personally. I are an engineer.

[Mark@EAC]

probably just a defect part, but be sure you are filling the system correctly. Low coolant will create a steam pocket that cannot escape the cap fast enough, and will pop the weakest link in the system.

[ZeroR2]

That's not very comforting when the plastic content of cars is increasing with each generation. You'd think that the design would take into account the change of materials, and that the engineers would get up to speed on the materials properties. Sheesh. I do take it personally. I are an engineer.

I am glad I don't have your problems. The reason why:

http://www.zionsvilleautosport.com/store/screen/prod/store_code/6134/product_code/AASETII.htm

[E39sofine]

That's not very comforting when the plastic content of cars is increasing with each generation. You'd think that the design would take into account the change of materials, and that the engineers would get up to speed on the materials properties. Sheesh. I do take it personally. I are an engineer.

I see your point, but I'm an engineer as well. And you have to take part defect probability into account. As well as the idea that they was still a learning curve for plastic parts that have to withstand prolonged exposure to the conditions under the hood for the e39. Let's face it. There are certain design standpoints (referring to the e39's plastic materials) that makes sense, others, could possibly be design flaws and need further attention. I mean, they didn't spend 20 years developing this vehicle, and as far as I'm concerned, they did an excellent job creating a well developed vehicle in the time they were given.

[Petes540i6]

It appears that both you and your expansion tank wanted to vent.